Internal magnet coaxial line device



W. C. HEITHAUS INTERNAL MAGNET COAXIAL LINE DEVICE Original Filed Jan.30, 1960 m2 .i @E 292m S MIE INVENTOR. WML/AM 0. HE/H/:Us

ATTORNEY Jan. 8, 1963 mmano NAL ZON: QN

United States Patent O 3,072,867 INTERNAL MAGNET COAXIAL LINE DEVICEWilliam C. Heithaus, Dunedin, Fla., assignor to Sperry Rand Corporation,a corporation of Delaware Original application Jan. 30, 1960, Ser. No.2,259. Divided and this application Mar. 28, 1962, Ser. No.

4 Claims. (Cl. S33-24.2)

This invention relates to magnetic circuits, and more particularly itconcerns an improved means for providing a magnetic bias to certainelectromagnetic wave devices.

The present application is a division of copending application S.N.2,259, filed January 30, 1960, and is particularly directed to aninternal magnet coaxial transmission line type of device, of which I amthe sole inventor. The present state of the art in microwave technologis characterized by extensive use of certain new materials which, whenmagnetically biased in the presence of miklators and attenuators, thematerial in the device is often Lbiased to a point where gyromagneticresonance occurs.

This may require magnetic field strengths in the order of 2,000oersteds. In order to provide these required values of magnetic fieldwithin the material to be biased, a magnet -larger than the deviceitself is sometimes necessary. Conventional biasing techniques generallyinvolve Vthe use of large horseshoe type magnets encasing the coaxialstructure. The size and configuration of these magnets present difficultproblems in weight, cooling and accessibility, and may render thesedevices impractical for certain applications.

A second disadvantage which, under certain circumstances, may be asgreat a detriment as required magnet size, is the susceptibility ofthese devices to stray magnetic fields. These stray fields will add toor detract from the magnetic biasing field and cause erratic operationof the material within the device.

Consequently, it is an object of this invention to provide alightweight, low-cost, means for effectively biasing a gyromagneticelement in a transverse electromagnetic mode propagating device.

It is a further object to provide a magnetically biased coaxial linetype device, wherein a smaller size and more effective cooling areobtained through the elimination of externally mounted magnets.

Another object of this invention is to provide a magnetically biasedcoaxial line type device which makes most efficient use of the biasingfield.

It is a still further object to provide such a device which issubstantially unaffected by stray magnetic fields.

These and other objects of the invention will become more apparent fromthe following description and claims.

Briefiy, this invention accomplishes its purpose in the followingmanner:

A permanent magnet is located Within the coaxial line device and isshaped and positioned to fit Within or to form the actual structure ofits center conductor. The magnet is oriented and located to properlydirect magnetic flux through the gyromagnetic material which is alsolocated within the device. The outer walls of the device may be of a lowmagnetic reluctance material to provide 'being located at the ends.

3,72,867 Patented Jan. 8, 1963 ICC an easy iiux return path and toshield the device from stray externally generated magnetic fields. TheWalls also have conductive internal surfaces in order to contain themicrowave field and to minimize electrical resistance losses in thesesurfaces.

In the drawings:

FIG. 1 is a longitudinal section view of one preferred embodiment of theinvention;

FIG. 2 is a cross sectional view taken along the line 2-2 of FIG. 1.

FIGS. 1 and 2 show an embodiment of the invention as applied to acoaxial line isolator. This is a non-recip rocal device which permitsmicrowave energy to flow in one direction but attenuates electromagneticWaves propagating in the opposite direction. The coaxial line y10 intowhich the device is integrated is seen to consist of a hollow tubularouter conductor 11 in coaxial alignment with and enclosing a cylindricalcenter conductor 12. The outer and inner conductors are electrically andmagnetically insulated from each other and thus define a high frequencytransverse electromagnetic mode propagating region in the space betweenthem.

Two strips 1S and 16 of ferromagnetic material are placed longitudinallyon either side of the center conductor. These strips are exposed to thepropagating microwave field and when magnetically biased under properconditions will either transmit or attenuate the field depending uponits sense of circular polarization. A dielectric insert 17 llsapproximately half the volume enclosed by the outer conductor 11 in thevicinity of the ferromagnetic strips 15 and 16. This insert serves todistort the incident microwave magnetic field configuration', which incoaxial line normally propagates in a transverse electromagnetic mode.The distortion is of such a nature that the field exhibits a circularlypolarized component. -This circular polarization is necessary fornonreciprocal action in gyromagnetic microwave devices.

A portion of the center conductor 12 in the area of the ferromagneticstrips 15 and 16 is removed and replaced by a permanent magnet 18 of thesame size and shape. Any magnetic material, such as Alnico may be usedfor this purpose so long as it can be magnetized sufficiently to providethe necessary bias to the ferro- ;magnetic strips. In practice, however,it has been found 45 that the grain oriented barium ferrite magnetsexhibit high coercive forces which make them more desirable for thesedevices. It is to be noted that for this application, the magnet 1S ispolarized with its poles running along opposite sides of its cylindricalsurface rather than Also, the poles are aligned lso as to directmagnetic flux through the ferromagnetic strips 15 and 16 in a directiontransverse to the flow of microwave energy. An electrically conductivefilm 19 is either painted or plated on the surfaces of the magnet 18.This provides an electrical continuation of the center conductor 12 ofthe coaxial line. This film of course would be unnecessary in the casewhere a permanent magnet material is chosen which has a surfaceconductivity approaching that of copper or silver.

A length of the outer conductor 11, also in the vicinity offerromagnetic strips, is removed and replaced by a tubular section 2f)of the same dimensions. This section is made of a low magneticreluctance material such as iron, and provides an effective return pathfor magnetic fiux. This makes more efficient use of the available fiuxwith consequent reduction in the required magnet size. Furthermore, thecomplete enclosure of the system by this material provides a magneticshield which protects the system from the effects of stray externalmagnetic fields. An electrically conductive film 21 is either painted orplated on the inside surface of the low reluctance outer section 20 inorder to provide an electrical continuation of the outer conductor ofthe line.

During operation of the device, microwave energy Originating at agenerator 13 travels toward a utilizaf tion means 14 via the coaxialline 10 in a TEM mode conguration. Upon encountering the dielectricinsert 17 the microwave magnetic iield is distorted in such a manner asto cause a circularly polarized component to be generated. The sense ofcircular polarization, however, is such that propagation of energytoward utilization means 14 will be relatively unaffected by theferromagnetic strps 15 and 16. Should any of this energy be reflected bydiscontinuities between the strips and the load, it will impinge uponthe isolator from the opposite direction. The sense of circularpolarization now will appear reversed to the ferromagnetic strips andresonant attenuation will occur, thus preventing this reflected energyfrom reaching the generator 13.

The magnetic ux which provides the necessary bias for the ferromagneticstrips 15 and 16 originates from the permanent magnet 18, which formsthe center conductor. The liux flows tirst through the upper strip 15into the low-reluctance section 20 of the outer tubular conductor 11, itthen travels around the conductor, through the lower strip 16, and againinto the magnetic source 18. The electrically conductive films 19 and 21on the permanent magnet and the lowreluctance magnetic outer conductorprovide an electrical continuation of the coaxial line, while allowingeasy passage of magnetic flux from the magnetic components to theferromagnetic strips.

While the invention has been described in its preferred embodiments itis to be understood that the words which have been used are words ofdescription rather than of limitation and that changes within thepurview of the appended claims may be made without departing from thetrue scope and spirit of the invention in its broader aspects.

What is claimed is:

1. A transverse electromagnetic wave transmission line devicecomprising, Y

rst and second longitudinally extending spaced-apart and conductivelyseparated electrical conductors for guiding electromagnetic waves in atransverse electromagnetic mode along a path defined by said conductors,

an element of magnetic polarizable gyromagnetic material that exhibitsgyromagnetic effects to electromagnetic waves propagating along saidconductors,

said gyromagnetic element being positioned between said conductors inthe propagating path of said waves, and a permanent magnet entirelyenclosed Within and separated from the propagating path of said waves byone of said conductors,

said permanent magnet being positioned in its enclosing conductor in theregion adjacent said gyromagnetic element and being magnetizedtransversely to said conductor to immerse said gyrornagnetic element ina transverse magnetic field.

2. The combination as claimed in claim 1 and further including,

a member of low magnetic reluctance material adjacent the other one ofsaid conductors and exterior to the propagating path of said waves,

said member of low reluctance material substantially enclosing saidconductors, thereby providing a low reluctance flux return path for themagnetic flux produced by said permanent magnet.

3. A coaxial transmission line nonreciprocal device comprising,

a section of coaxial transmission line having longitudinally extendinginner and outer conductors conductively separated from each other forpropagating electromagnetic waves in a transverse electromagnetic mode,

mode distorting means disposed between said conductors and incompletelyfilling the cross-sectional area therebetween for distorting saidtransverse electromagnetic mode to produce circularly polarizedcomponents of said electromagnetic waves,

at least one element of magnetic polarizable gyromagnetic material thatexhibits gyromagnetic effects to waves propagating through said line,

said gyromagnetic element being positioned between said conductors inthe region of circular polarization of waves propagating through saidline,

a permanent magnet located entirely within said inner conductor in theregion occupied by said element of gyromagnetic material and magnetizedtransversely to said transmission line for transversely magnetizing saidgyromagnetc element, and

a tubular element of a low magnetic reluctance material surrounding saidouter conductor for providing a low reluctance magnetic flux return pathfor the magnetic flux produced by said permanent magnet.

4. The combination claimed in claim 3 wherein said permanent magnet is alongitudinally extending bar magnet magnetized transversely to itslongitudinal dimension.

No references cited.

1. A TRANSVERSE ELECTROMAGNETIC WAVE TRANSMISSION LINE DEVICECOMPRISING, FIRST AND SECOND LONGITUDINALLY EXTENDING SPACED-APART ANDCONDUCTIVELY SEPARATED ELECTRICAL CONDUCTORS FOR GUIDING ELECTROMAGNETICWAVES IN A TRANSVERSE ELECTROMAGNETIC MODE ALONG A PATH DEFINED BY SAIDCONDUCTORS, AN ELEMENT OF MAGNETIC POLARIZABLE GYROMAGNETIC MATERIALTHAT EXHIBITS GYROMAGNETIC EFFECTS TO ELECTROMAGNETIC WAVES PROPOGATINGALONG SAID CONDUCTORS, SAID GYROMAGNETIC ELEMENT BEING POSITIONEDBETWEEN SAID CONDUCTORS IN THE PROPAGATING PATH OF SAID WAVES, AND APERMANENT MAGNET ENTIRELY ENCLOSED WITHIN AND SEPARATED FROM THEPROPAGATING PATH OF SAID WAVES BY ONE OF SAID CONDUCTORS, SAID PERMANENTMAGNET BEING POSITIONED IN ITS ENCLOSING CONDUCTOR IN THE REGIONADJACENT SAID GYROMAGNETIC ELEMENT AND BEING MAGNETIZED TRANSVERSELY TOSAID CONDUCTOR TO IMMERSE SAID GYROMAGNETIC ELEMENT IN A TRANSVERSEMAGNETIC FIELD.